scholarly journals Competition, Nodule Occupancy, and Persistence of Inoculant Strains: Key Factors in the Rhizobium-Legume Symbioses

2021 ◽  
Vol 12 ◽  
Author(s):  
Marcela Mendoza-Suárez ◽  
Stig U. Andersen ◽  
Philip S. Poole ◽  
Carmen Sánchez-Cañizares
Keyword(s):  
Nitrogen Fixation ◽  
Current Knowledge ◽  
Local Environment ◽  
Nitrogen Fertilizers ◽  
Superior Performance ◽  
Nodule Occupancy ◽  
Inoculant Strain ◽  
Native Strains ◽  
Biological Nitrogen ◽  
Rhizobial Inoculants

Biological nitrogen fixation by Rhizobium-legume symbioses represents an environmentally friendly and inexpensive alternative to the use of chemical nitrogen fertilizers in legume crops. Rhizobial inoculants, applied frequently as biofertilizers, play an important role in sustainable agriculture. However, inoculants often fail to compete for nodule occupancy against native rhizobia with inferior nitrogen-fixing abilities, resulting in low yields. Strains with excellent performance under controlled conditions are typically selected as inoculants, but the rates of nodule occupancy compared to native strains are rarely investigated. Lack of persistence in the field after agricultural cycles, usually due to the transfer of symbiotic genes from the inoculant strain to naturalized populations, also limits the suitability of commercial inoculants. When rhizobial inoculants are based on native strains with a high nitrogen fixation ability, they often have superior performance in the field due to their genetic adaptations to the local environment. Therefore, knowledge from laboratory studies assessing competition and understanding how diverse strains of rhizobia behave, together with assays done under field conditions, may allow us to exploit the effectiveness of native populations selected as elite strains and to breed specific host cultivar-rhizobial strain combinations. Here, we review current knowledge at the molecular level on competition for nodulation and the advances in molecular tools for assessing competitiveness. We then describe ongoing approaches for inoculant development based on native strains and emphasize future perspectives and applications using a multidisciplinary approach to ensure optimal performance of both symbiotic partners.

Increasing biological nitrogen fixation by white clover-rhizobia symbiosis

2019 ◽  
pp. 231-234 ◽  
Author(s):  
Shengjing Shi ◽  
Laura Villamizar ◽  
Emily Gerard ◽  
Clive Ronson ◽  
Steve Wakelin ◽  
...  
Keyword(s):  
Nitrogen Fixation ◽  
White Clover ◽  
Biological Nitrogen Fixation ◽  
Root Nodules ◽  
N Fixation ◽  
Nodule Occupancy ◽  
Coating Technology ◽  
Vitro Assay ◽  
Biological Nitrogen

Biological nitrogen fixation (BNF) is the process of converting atmospheric nitrogen to ammonia through legume–rhizobia symbiosis. The nitrogen fixed by rhizobia in root nodules is available for plant use. This process can be harnessed to improve N fertility on farm. Field surveys across New Zealand (NZ), within a farm and within paddocks, have revealed large spatial variability of rhizobial population size and symbiotic effectiveness with white clover. These results indicate that naturalised rhizobia may not be supporting optimal BNF. Over 500 strains of clover-nodulating rhizobia were isolated from NZ pasture soils, with more than 90 demonstrating greater N-fixation capacity with white clover than the commercial inoculant strain TA1. Seven NZ isolates were tested for nodule occupancy and all seven had significantly higher occupancy rates than TA1 in an in vitro assay, indicating increased competitiveness of those strains. In addition, novel seed-coating technology improved the survival of TA1 and isolate S10N9 from 1 month to more than 4 months compared with a standard coating formulation. There is potential to increase the symbiotic capacity of white clover in pastures through use of more effective and competitive rhizobial strains, along with their improved survival on seed provided by a new coating technology.

scholarly journals Potential of Rhizobium sullae–Sulla coronaria Symbiotic Biological Nitrogen Fixation to Supplement Synthetic Mineral Nitrogen in Olive Tree Fertilization

Agronomy ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 270
Author(s):  
Biagi Angelo Zullo ◽  
Gino Ciafardini
Keyword(s):  
Nitrogen Fixation ◽  
Green Manure ◽  
Organic Nitrogen ◽  
Indigenous Population ◽  
Olive Tree ◽  
Organic Fertilizers ◽  
Nitrogen Fertilizers ◽  
Nodule Formation ◽  
Biological Nitrogen ◽  
Sulla Coronaria

The aim of the present work is to compare olive tree nitrogen fertilization over two years of trials, using synthetic chemical fertilizers along with organic fertilizers composed of the green manure of sulla (Sulla coronaria) inoculated with the symbiont Rhizobium sullae or left uninoculated. The tests indicated that symbiotic nitrogen fixation promoted by the sulla–R. sullae symbiosis represents an important source of nitrogen that can replace or supplement synthetic nitrogen fertilizers for olive tree cultivation when sulla is inoculated with R. sullae in a soil already populated by the symbiont. Integration of the indigenous population of R. sullae via sulla inoculation with a selected strain yielded nodule formation in 100% of plants and produced a sufficient amount of biomass rich in nitrogen with a low C/N ratio. On the contrary, olive tree fertilization using the green manure of sulla that was not inoculated with the symbiont supplied significantly less organic nitrogen in 2017 and 2018, respectively, compared to the control. Optimal management of the multi-factorial approaches involved in green manure olive fertilization are also reported.

scholarly journals Engineering Nitrogen Fixation Activity in an Oxygenic Phototroph

2018 ◽  
Author(s):  
Deng Liu ◽  
Michelle Liberton ◽  
Jingjie Yu ◽  
Himadri B. Pakrasi ◽  
Maitrayee Bhattacharyya-Pakrasi
Keyword(s):  
Nitrogen Fixation ◽  
Energy Demand ◽  
Nitrogenase Activity ◽  
Crop Plants ◽  
Nitrogen Fertilizers ◽  
Nitrogen Fixation Activity ◽  
Fixation Activity ◽  
Photosynthetic Organism ◽  
Biological Nitrogen ◽  
Oxygenic Phototroph

ABSTRACTBiological nitrogen fixation is catalyzed by nitrogenase, a complex metalloenzyme found only in prokaryotes. N2fixation is energetically highly expensive, and an energy generating process such as photosynthesis can meet the energy demand of N2fixation. However, synthesis and expression of nitrogenase is exquisitely sensitive to oxygen. Thus, engineering nitrogen fixation activity in photosynthetic organisms that produce oxygen is challenging. Cyanobacteria are oxygenic photosynthetic prokaryotes, and some of them also fix N2. Here, we demonstrate a feasible way to engineer nitrogenase activity in the non-diazotrophic cyanobacteriumSynechocystissp. PCC 6803 through the transfer of 35 nitrogen fixation (nif) genes from the diazotrophic cyanobacteriumCyanothecesp. ATCC 51142. In addition, we have identified the minimalnifcluster required for such activity inSynechocystis6803. Moreover, nitrogenase activity was significantly improved by increasing the expression levels ofnifgenes. Importantly, the O2tolerance of nitrogenase was enhanced by introduction of uptake hydrogenase genes, showing this to be a functional way to improve nitrogenase enzyme activity under micro-oxic conditions. To date, our efforts have resulted in engineeredSynechocystis6803 strains that remarkably have more than 30% N2-fixation activity compared to that inCyanothece51142, the highest such activity established in any non-diazotrophic oxygenic photosynthetic organism. This study establishes a baseline towards the ultimate goal of engineering nitrogen fixation ability in crop plants.IMPORTANCEApplication of chemically synthesized nitrogen fertilizers has revolutionized agriculture. However, the energetic costs of such production processes as well as the wide spread application of fertilizers have raised serious environmental issues. A sustainable alternative is to endow crop plants the ability to fix atmospheric N2in situ. One long-term approach is to transfer allnifgenes from a prokaryote to plant cells, and express nitrogenase in an energy-producing organelle, chloroplast or mitochondrion. In this context,Synechocystis6803, the non-diazotrophic cyanobacterium utilized in this study, provides a model chassis for rapid investigation of the necessary requirements to establish diazotrophy in an oxygenic phototroph.

scholarly journals Manipulating nitrogen regulation in diazotrophic bacteria for agronomic benefit

2019 ◽  
Vol 47 (2) ◽  
pp. 603-614 ◽  
Author(s):  
Marcelo Bueno Batista ◽  
Ray Dixon
Keyword(s):  
Nitrogen Fixation ◽  
Genetic Manipulation ◽  
Current Knowledge ◽  
Ammonia Excretion ◽  
Ammonium Assimilation ◽  
Regulatory Mechanisms ◽  
Diazotrophic Bacteria ◽  
Fixed Nitrogen ◽  
Regulatory Circuits ◽  
Biological Nitrogen

AbstractBiological nitrogen fixation (BNF) is controlled by intricate regulatory mechanisms to ensure that fixed nitrogen is readily assimilated into biomass and not released to the environment. Understanding the complex regulatory circuits that couple nitrogen fixation to ammonium assimilation is a prerequisite for engineering diazotrophic strains that can potentially supply fixed nitrogen to non-legume crops. In this review, we explore how the current knowledge of nitrogen metabolism and BNF regulation may allow strategies for genetic manipulation of diazotrophs for ammonia excretion and provide a contribution towards solving the nitrogen crisis.

Issues affecting the competitiveness of white clover rhizobia in New Zealand pastures

1996 ◽  
Vol 6 ◽  
pp. 87-90
Author(s):  
C.W. Ronson ◽  
W.L. Lowther
Keyword(s):  
Nitrogen Fixation ◽  
New Zealand ◽  
White Clover ◽  
Symbiotic Nitrogen Fixation ◽  
Genetic Interactions ◽  
Indigenous Populations ◽  
Nodule Occupancy ◽  
Rhizobial Strain ◽  
Specific Host ◽  
Inoculant Strain

Research into improving symbiotic nitrogen fixation of white clover in New Zealand pastures through the introduction of effective rhizobia is reviewed. Naturalised populations of rhizobia are usually highly diverse and of reduced effectiveness compared to inoculant strains, and large increases in nitrogen fixed have been found in situations where high nodule occupancy by an inoculant strain was obtained. The likelihood of an inoculant strain initially forming a high proportion of nodules is dependent on the size of the naturalised and inoculant populations, and the strain of rhizobia. Lack of persistence of the inoculant strain in competition with naturalised rhizobia also limits improvement of symbiotic nitrogen fixation in pasture through inoculation. Recent studies suggest that genetic instability of inoculant strains and exchange of symbiotic plasmids contribute to the diversity of naturalised populations and lack of inoculant persistence. Therefore, it is necessary to understand the ecology of naturalised populations, including their genetic interactions with inoculant strains, in order to develop strategies to improve the competitiveness and persistence of inoculant strains. Alternatively it may be possible to increase the effectiveness of indigenous populations through gene transfer from the inoculant strain. The possibility of breeding specific host cultivar/rhizobial strain combinations also merits further research. Keywords: competition, genetic stability, inoculation, nitrogen fixation, rhizobia, white clover

Novel rhizobia exhibit superior nodulation and biological nitrogen fixation even under high nitrate concentrations

2019 ◽  
Vol 96 (2) ◽  
Author(s):  
Hien P Nguyen ◽  
Hiroki Miwa ◽  
Jennifer Obirih-Opareh ◽  
Takuya Suzaki ◽  
Michiko Yasuda ◽  
...  
Keyword(s):  
Nitrogen Fixation ◽  
Bradyrhizobium Japonicum ◽  
Root Nodules ◽  
Nitrogen Fertilizers ◽  
Nodule Formation ◽  
Nitrogen Fixing ◽  
Nitrogen Fixation Activity ◽  
Nitrate Concentrations ◽  
Nodulation Competitiveness ◽  
Biological Nitrogen

ABSTRACT Legume–rhizobium symbiosis leads to the formation of nitrogen-fixing root nodules. However, externally applied chemical nitrogen fertilizers (nitrate and ammonia) strongly inhibit nodule formation and nitrogen fixation. Here, we isolated several rhizobial strains exhibiting a superior nodulation and nitrogen fixation with soybean at high nitrate concentrations. The nodulation of soybean symbiont Bradyrhizobium diazoefficiens USDA110 was significantly inhibited at 12.5 mM nitrate; however, three isolates (NKS4, NKM2 and NKTG2) were capable of forming nitrogen-fixing nodules, even at 20 mM nitrate. These isolates exhibited higher nodulation competitiveness and induced larger nodules with higher nitrogen-fixation activity than USDA110 at 5 mM nitrate. Furthermore, these isolates induced more nodules than USDA110 even in nitrate-free conditions. These isolates had a distant lineage within the Bradyrhizobium genus; though they were relatively phylogenetically close to Bradyrhizobium japonicum, their morphological and growth characteristics were significantly different. Notably, in the presence of nitrate, expression of the soybean symbiosis-related genes (GmENOD40 and GmNIN) was significantly higher and expression of GmNIC1 that is involved in nitrate-dependent nodulation inhibition was lower in the roots inoculated with these isolates in contrast with inoculation of USDA110. These novel rhizobia serve as promising inoculants for soybeans cultivated in diverse agroecosystems, particularly on nitrate-applied soils.

Nitrogen Fixation and Diazotrophs – A Review

2021 ◽  
Vol 26 (4) ◽  
pp. 2834-2845
Author(s):  
WENLI SUN ◽  
MOHAMAD HESAM SHAHRAJABIAN ◽  
QI CHENG
Keyword(s):  
Nitrogen Fixation ◽  
Plant Growth Promoting Rhizobacteria ◽  
Nitrogen Fertilizers ◽  
Sulfate Reducing ◽  
Fe Protein ◽  
Different Seasons ◽  
Plant Growth Promoting ◽  
Accepted Practice ◽  
Metal Cofactors ◽  
Biological Nitrogen

Nitrogen fixation involves formation of ammonium from N2, which needs a high input of energy. Biological nitrogen fixation utilizes the enzyme nitrogenase and ATP to fix nitrogen. Nitrogenase contains a Fe-protein and a Mo-Fe-protein and other metal cofactors. Soil diazotrophs possess the function of fixing atmospheric N2 into biologically available ammonium in ecosystems. In Aechaea, nitrogen fixation has been reported in some methanogens such as Methanobacteriales, Methanococcales, and Methanosarcinales. Community structure and diversity of diazotrophic are correlated with soil pH. All known organisms which involve in nitrogen-fixing which are called diazatrophs are prokaryotes, and both bacterial and archaeal domains are responsible for that. Diazotrophs are categorized into two main groups namely: root-nodule bacteria and plant growth-promoting rhizobacteria. Diazotrophs include free living bacteria, such as Azospirillum, Cupriavidus, and some sulfate reducing bacteria, and symbiotic diazotrophs such Rhizobium and Frankia. Two important parameters which may affect diazotroph communities are temperature and soil moisture in different seasons. To have sustainable agriculture, replacing expensive chemical nitrogen fertilizers with environmentally friendly ways is the most accepted practice.

Orientation of processes of biological nitrogen transformation in winter rye agroecosystems under different levels of fertilization background

2016 ◽  
Vol 3 (3) ◽  
pp. 28-34
Author(s):  
V. Volkogon ◽  
I. Korotka
Keyword(s):  
Root Zone ◽  
Field Studies ◽  
Nitrogen Transformation ◽  
Mineral Nitrogen ◽  
Nitrogen Fertilizers ◽  
Winter Rye ◽  
Podzolic Soils ◽  
Microbial Preparation ◽  
Biological Nitrogen

Aim. To determine physiologically expedient rates of mineral nitrogen in winter rye production on sod-podzol- ic soils based on the orientation of the processes of biological nitrogen transformation in the plants rhizosphere. Methods. Field studies, gas chromatography determination of potential nitrogen fi xation activity and potential emissions of N 2 O. Results. The results obtained have demonstrated that the rates of mineral nitrogen, not ex- ceeding 60 kg/ha, can be considered physiologically expedient for winter rye production on sod-podzolic soils. Under the application of microbial preparation Diazobakteryn, there is a higher physiological need of plants for nitrogen, which allows increasing the rates of nitrogen fertilizers up to 90 kg/ha. Conclusions. The orienta- tion of the processes of biological nitrogen transformation in the root zone of plants is a reliable indicator of determining the appropriateness of nitrogen fertilization of crops.

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